Tire tread is expected to maintain excellent steering stability (steering stability performance) in a wide range of air temperature and in a wide range of road surface temperature. In other words, tire tread is expected to maintain stable steering stability (excellent steering stability in terms of temperature dependence) not only on a low-temperature road surface in winter but also on a high-temperature road surface in summer.
Conventionally, in order to improve steering stability on a high-temperature road surface a method in which a liquid polymer, in addition to an oil, is blended as a softener to a rubber composition for tread or a method in which a resin is blended has been attempted. On the other hand, in order to improve steering stability on a low-temperature road surface a method in which a low-temperature softener is blended has been studied.
However, there is a problem that the content of the low-temperature softener which is blended for the purpose of improving performance on a low-temperature road surface is, compared to oil, more likely to be reduced by transferring to neighboring members and by volatilization, and as a result, the rubber becomes hardened and steering stability tends to deteriorate.
Although JP 2012-162620 A describes a rubber composition for tread which contains a certain resin and softener, temperature dependence of steering stability has not been considered.